Study of Time and Frequency Domain Channel Estimation for OFDM Systems

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In wireless communication environments, the channel must be estimated for equalization in the receiver. The accuracy of channel information affects the system performance. In this thesis, we will introduce and analyze a simple channel impulse response (CIR) estimation method in which a unit pulse followed by a series of consecutive zeros is inserted ahead of each time domain OFDM block signal. Another more popular method is to estimate the channel frequency response (CFR) in which some pilot symbols are inserted in the frequency-domain signal, and we refer to it as “FD estimation”. For the CIR estimation method, we can directly transmit one pulse before every data block. In this thesis, we call it “TD estimation”. At the receiver, we can easily obtain the whole instant CIR and decide the path number. Unlike the TD estimation, FD estimation just only estimates the CFR at pilot sub-channels. The CFR at other sub-channels are obtained by interpolation or least-squares fitting, linear minimum mean-squares error and so on. In this thesis, we will compare the performance between TD and FD estimation. Finally, we study the performance of TD estimation in a slow time-variant multipath channel. We use the linear interpolation method to approximate the variation of CIR. And then a simple frequency-domain equalizer technique is also introduced to compensate the effect of interchannel interference (ICI) due to time-variant channel.